Chronic hepatic failure and acute ammonia intoxication are serious diseses involving abnormally high blood-ammonia levels. Acute alcoholic coma obviously results from markedly elevated tissue alcohol levels. Previous methods for treating patients having such diseases include: dietary protein restriction, antibiotic administration, hemedialysis, extracorporeal ion-exchange blood shunts, and finally, transplantation of donor liver. The blood shunt involves passing blood through an external shunt loaded with micro-capsules containing ion-exchange resins which remove the ammonia and replace it with sodium ions. As well as involving aseptic surgical techniques and providing only periodic relief, the external shunt may lead to high blood sodium levels.
Recent developments in methods for urea removal in hemodialysis involve the action of urease on urea with the release of large quantities of ammonia as a product. The presence of a high ammonia concentration in the dialysate rapidly leads to reverse dialysis of ammonia and marked increases in the patient's blood ammonia level. To prevent this from happening, the released ammonia is then either adsorbed or trapped by microencapsulated cation exchange resin [Chang, T.M.S., Semi-permeable Aqueous Microcapsules "Artificial Cells": With Emphasis on Experiments in an Extracorporeal Shunt System, Trans, Amer. Soc. Artif. Int. Organs, 12:13-19 (1966); Sparks, R. E., Solemme, R. M., Meier, P. M. Litt, M. H. and Lindan, O., Removal of Waste Metabolities in Uremia by Microencapsulated Reactants, Trans. Amer. Soc. Artif, Int. Organs, 15:353-58 (1969)], or by zirconium phosphate [Gordon, A., Greenbaum, M. A., Marantz, L. B., McArthur, M. and Maxwell, M. H., A Sorbent-based Low-Volume Recirculating Dialysate System Trans. Amer. Soc. Artif, Int. Organs, 15:347-52 (1969); Greenbaum, M. A. and Gordon, A., A. Regenerative Dialysis Supply System, Dial. Transpl., 1:18-30 (1972 )]. The zirconium phosphate system also includes activated carbon and zirconium oxide and urease to convert urea in dialysate to ammonium carbonate. This system was developed by the Marquardt Co. in Van Nuys, California, under the trademark REDY. These systems have the advantage that a small volume of water (tap), which is recycled, can replace very large volumes of expensive dialysis fluid. The bulk of equipment is thus also markedly reduced. The major difficulty of this adsorption or ion exchange method is that the sorbent becomes saturated with ammonium ions during dialysis and cannot be regenerated in practice. The sorbent loaded cartridge needs to be repeatedly replaced. This becomes expensive and reduces one of the main potential advantages of the method.
Most of the above methods are short-range periodic treatments and are still in the experimental stage.